Radio transmitter with reduced power consumption

ABSTRACT

A technique for controlling a transmitter apparatus is useful for reducing power consumption, and may be particularly applicable to portable apparatuses such as mobile transceivers which employ a battery power supply. According to an exemplary embodiment, the transmitter apparatus includes a power amplifier for amplifying a transmission signal. A processor controls the power amplifier based on a type of digital modulation associated with the transmission signal.

The present invention generally relates to transmitter apparatuses, andmore particularly, to a technique for controlling the power consumptionof a transmitter apparatus. The present invention may be particularlyapplicable to portable apparatuses such as mobile transceivers whichutilize a battery power supply.

Certain communication standards may require apparatuses to support aplurality of different types of signal modulation. For example, wirelesscommunication standards such as Hiperlan2, IEEE 802.11a, DVB-T and/orother standards specify different types of modulation to be useddepending on the data transmission rate employed. Table 1 below showsexemplary types of modulation and corresponding data transmission ratesthat may be specified by such communication standards. TABLE 1Modulation Type Data Transmission Rate (Mbps) BPSK ½ 6 BPSK ¾ 9 QPSK ½12 QPSK ¾ 18 16 QAM ½ 24 16 QAM ¾ 36 64 QAM ⅔ 48 64 QAM ¾ 54

The modulation types shown in Table 1 employ the general principles ofOrthogonal Frequency Division Multiplexing modulation (OFDM), which mayrequire the use of a power amplifier for signal transmission having alinear relationship between input power and output power. To satisfythis linearity requirement, such amplifiers typically require a highbias current during a transmitting mode, and may therefore consume arelatively large amount of power. For example, a power amplifier havinga gain of 10 dB may require a bias current of 150 mA or more during thetransmitting mode in order to operate at 5 GHz, which is a typicalfrequency range for communication standards such as Hiperlan2 and IEEE802.11a. This requirement of a high bias current for the power amplifiermay significantly increase the overall power consumption of an apparatusduring the transmitting mode. For example, with an apparatus such as amobile transceiver, the peak power consumed by the power amplifier mayconstitute 70% or more of the total power consumption of the apparatusduring the transmitting mode. Accordingly, the power amplifier used forsignal transmission may consume a large of amount of power, which may beparticularly problematic for portable apparatuses such as mobiletransceivers that utilize a battery power supply. Moreover, the powerconsumption of the power amplifier may also cause the apparatus togenerate heat in an undesirable manner.

Accordingly, there is a need for a technique for controlling transmitterapparatuses which avoids the foregoing problems, and thereby reducespower consumption. The present invention may address these and/or otherissues.

In accordance with an aspect of the present invention, an apparatushaving a signal transmission function is disclosed. According to anexemplary embodiment, the apparatus comprises amplifying means foramplifying a transmission signal. Processing means are provided forcontrolling the amplifying means based on a type of digital modulationassociated with the transmission signal.

In accordance with another aspect of the present invention, a method forcontrolling a transmitter apparatus is disclosed. According to anexemplary embodiment, the method comprises steps of identifying a typeof digital modulation for a transmission signal, and controlling poweramplification of the transmission signal based on the type of digitalmodulation.

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a block diagram of a transmitter apparatus according to anexemplary embodiment of the present invention;

FIG. 2 is a diagram illustrating further exemplary details of the poweramplifier of FIG. 1;

FIG. 3 is a graph illustrating exemplary power input/outputcharacteristics; and

FIG. 4 is a flowchart illustrating steps according to an exemplaryembodiment of the present invention.

The exemplifications set out herein illustrate preferred embodiments ofthe invention, and such exemplifications are not to be construed aslimiting the scope of the invention in any manner.

Referring now to the drawings, and more particularly to FIG. 1, atransmitter apparatus 100 according to an exemplary embodiment of thepresent invention is shown. In FIG. 1, transmitter apparatus 100comprises processing and memory means such as processor and memory 10,modulating means such as modulator 20, variable amplifying means such asvariable gain amplifier (VGA) 30, frequency converting means such asfrequency up converter 40, power amplifying means such as poweramplifier 50, digital-to-analog converting means such asdigital-to-analog converter (DAC) 60, and signal transmitting means suchas signal transmitting element 70. Some of the foregoing elements ofFIG. 1 may for example be embodied using one or more integrated circuits(ICs). For clarity of description, certain conventional elementsassociated with transmitter apparatus 100 such as control signals, powersignals, and/or other conventional elements may not be shown in FIG. 1.According to an exemplary embodiment, transmitter apparatus 100 of FIG.1 may be part of a transceiver apparatus which also includes signalreceiving and processing elements not shown in FIG. 1. For example,transmitter apparatus 100 may be part of a mobile wireless transceiversuch as a telephone, pager, personal digital assistant (PDA) and/orother device.

Processor and memory 10 are operative to perform various functionsincluding processing, control and data storage functions. According toan exemplary embodiment, processor 10 is operative to process basebandsignals such as audio, video, text and/or other types of input signals,and thereby generate processed signals. Processor 10 is furtheroperative to identify a type of digital modulation to be used for atransmission signal of transmitter apparatus 100. According to anexemplary embodiment, processor 10 identifies the type of digitalmodulation to be used for a transmission signal by detecting andprocessing data included within one or more data frames provided fromsignal receiving and processing elements (not shown in FIG. 1)associated with transmitter apparatus 100. The type of digitalmodulation used by transmitter apparatus 100 may for example changebased on factors such as transmission range, the amount of data to betransmitted, and/or other factors. Memory 10 is operative to store dataincluding digital values which may be retrieved by processor 10 and usedto control power amplifier 50.

Modulator 20 is operative to modulate the processed signals providedfrom processor 10, and thereby generate modulated signals. According toan exemplary embodiment, modulator 20 is operative to perform aplurality of different types of modulation including various types ofOFDM, such as the types of bi-phase shift keyed (BPSK) modulation,quadrature phase shift keyed (QPSK) modulation, and/or quadratureamplitude modulation (QAM) shown in Table 1 herein. Accordingly,modulator 20 may be operative to process I and Q signals. Although notexpressly indicated in FIG. 1, the type of modulation performed bymodulator 20 may be adaptively controlled by a control signal providedfrom a processor, such as processor 10.

VGA 30 is operative to variably amplify the modulated signals providedfrom modulator 20, and thereby generate amplified signals. Although notexpressly indicated in FIG. 1, the gain of VGA 30 may be adaptivelycontrolled by a control signal provided from a processor, such asprocessor 10.

Frequency up converter 40 is operative to increase the frequency of theamplified signals provided from VGA 30. According to an exemplaryembodiment, frequency up converter 40 is operative to convert thefrequency of the amplified signals provided from VGA 30 to radiofrequency (RF) and/or microwave signals.

Power amplifier 50 is operative to amplify the power of the signalsprovided from frequency up converter 40, and thereby generate amplifiedtransmission signals. According to an exemplary embodiment, poweramplifier 50 comprises a plurality of cascaded stages, and generallyrequires linearity between its input power and output power. Accordingto principles of the present invention, a bias current of the finalstage of power amplifier 50 may be adaptively controlled based on thetype of digital modulation used by transmitter apparatus 100, which maysignificantly reduce the power consumption of power amplifier 50.Further details of power amplifier 50 will be provided later herein.

DAC 60 is operative to convert signals from a digital format to ananalog format. According to an exemplary embodiment, DAC 60 is operativeto convert digital values provided from processor 10 to analog signalswhich are used to control a bias current associated with power amplifier50.

Signal transmitting element 70 is operative to transmit the amplifiedtransmission signals provided from power amplifier 50, and may beembodied as any type of signal transmitting element such as an antenna,output terminal and/or other element. According to an exemplaryembodiment, signal transmitting element 70 is operative to wirelesslytransmit signals.

Referring now to FIG. 2, further exemplary details of power amplifier 50of FIG. 1 are provided. In particular, FIG. 2 shows the final stage of aplurality of cascaded stages (e.g., 3 stages) of power amplifier 50according to an exemplary embodiment of the present invention. In FIG.2, power amplifier 50 comprises capacitors C1 to C4, transistors Q1 andQ2, radial stubs RS1 and RS2, resistors R1 to R5, quarter wavelengthstubs S1 to S6, and voltage inputs V1 and V2. As indicated in FIG. 2,power amplifier 50 also includes input terminals for receiving inputsfrom frequency up converter 40 and DAC 60, and an output terminal forproviding an output to signal transmitting element 70. According to anexemplary embodiment, transistor Q2 is a field effect transistor (FET)constructed using GaAs. The specific values selected for the elements ofpower amplifier 50 may be a matter of design choice.

Transmitter apparatus 100 of FIG. 1 includes a parameter known as the“crest factor” (also known as the “back-off”) which is defined as theratio between its peak output power and average output power. The crestfactor is related to another parameter known as the “compression point”which represents a saturation point where the linear gain of transmitterapparatus 100 has been reduced by 1 dB. In other words, the compressionpoint indicates the introduction of non-linear effects between inputpower and output power. Such non-linear effects are shown in FIG. 3which provides a graph 300 illustrating exemplary power input/outputcharacteristics. As shown in FIG. 3, line 3A shows a linear relationshipbetween input power and output power (i.e., gain of 10 dB), while line3B shows the introduction of non-linear effects between input power andoutput power.

According to principles of the present invention, it has been determinedthat the crest factor varies based on the type of digital modulationused for transmission. Tables 2 to 4 below provide simulation resultsillustrating how the crest factor may vary depending on the type ofdigital modulation employed. TABLE 2 64 QAM ¾ Crest Factor (dB) SNR@10⁻⁴BER Loss (dB) Infinite 18.2 10.0  18.4 0.2 9.0 18.7 0.5 8.0 19.3 1.1 7.021.2 3.0 6.0 25.9 7.7

TABLE 3 16 QAM ¾ Crest Factor (dB) SNR@10⁻⁴ BER Loss (dB) Infinite 12.59.0 12.6 0.1 8.0 12.6 0.1 7.0 12.6 0.1 6.0 13.0 0.5 5.0 13.9 1.4

TABLE 4 QPSK ¾ Crest Factor (dB) SNR@10⁻⁴ BER Loss (dB) Infinite 6.2 8.06.3 0.1 7.0 6.3 0.1 6.0 6.4 0.2 5.0 6.5 0.3 4.0 6.6 0.4

In Tables 2 to 4 above, the losses correspond to values deduced from thesignal-to-noise ratio (SNR) of an ideal transmitter power amplifier(with infinite back-off) for a targeted bit error rate (BER) of 10⁻⁴ atthe output of a transceiver which includes transmitter apparatus 100,and signal receiving and processing elements (not shown in FIG. 1).Assuming an admitted loss up to 0.5 dB, Tables 2 and 4 indicate that thecrest factor may vary 5.0 dB between the 64 QAM ¾ modulation type andthe QPSK ¾ modulation type.

The variation of the crest factor based on the type of digitalmodulation, as represented in Tables 2 to 4, indicates that thecompression point may also vary depending on the type of digitalmodulation. With transmitter apparatus 100, power amplifier 50 may beresponsible for defining the compression point. In particular, it may bethe final stage of power amplifier 50 shown in FIG. 2 which primarilydefines the compression point for transmitter apparatus 100. Accordingto principles of the present invention, the bias current of the finalstage of power amplifier 50 shown in FIG. 2 may be decreased (therebydecreasing the compression point) when decreasing the efficiency per bitof the digital modulation, such as when changing the modulation from 64QAM ¾ to BPSK ½. By decreasing the bias current, the power consumptionof power amplifier 50 is reduced which may be particularly beneficialfor apparatuses such as mobile transceivers which employ a battery powersupply. The reduction of power consumption may also help reduce thegeneration of undesirable heat.

The following example illustrates how power consumption may be reducedaccording to the present invention. Consider a transceiver whichincludes transmitter apparatus 100 and that uses a half duplex mode inwhich the transmission time is 50%. Assume that the total powerconsumption of the transceiver in the transmitting mode is 200 mA, whichincludes the bias current of the final stage of power amplifier 50.Further assume that the estimated bias current of the final stage ofpower amplifier 50 is 150 mA when 64 QAM ¾ modulation is used, and is100 mA when BPSK ½ modulation is used. Accordingly, a current reductionof 50 mA is achieved when the transceiver is switched from 64 QAM ¾modulation to BPSK ½ modulation. This current reduction corresponds to25% of the total power consumption in the transmitting mode, whichcorresponds to a total reduction of 12.5% given the transmission time of50%.

According to principles of the present invention, the bias current ofthe final stage of power amplifier 50 shown in FIG. 2 may also beincreased (thereby increasing the compression point) when increasing theefficiency per bit of the digital modulation, such as when changing themodulation from BPSK ½ to 64 QAM ¾. In this manner, the presentinvention controls the bias current of the final stage of poweramplifier 50 in an adaptive manner and may thereby optimize the biascurrent for the particular type of digital modulation employed.

To facilitate a better understanding of the inventive concepts of thepresent invention, a more concrete example will now be provided.Referring now to FIG. 4, a flowchart 400 illustrating steps according toan exemplary embodiment of the present invention is shown. For purposesof example and explanation, the steps of FIG. 4 will be described withreference to transmitter apparatus 100 of FIG. 1 and power amplifier 50of FIG. 2. The steps of FIG. 4 are merely exemplary, and are notintended to limit the present invention in any manner.

At step 410, the type of digital modulation for a transmission signal isidentified. According to an exemplary embodiment, processor 10identifies the type of digital modulation at step 410 by detecting andprocessing data included within one or more data frames provided fromone or more signal receiving and processing elements (not shown inFIG. 1) associated with transmitter apparatus 100. As previouslyindicated herein, the type of digital modulation used by transmitterapparatus 100 may for example change based on factors such astransmission range, the amount of data to be transmitted, and/or otherfactors.

At step 420, a digital value is retrieved for the type of digitalmodulation identified at step 410. According to an exemplary embodiment,processor 10 retrieves the digital value at step 420 from memory 10, andthe digital value is based on the crest factor associated with the typeof digital modulation identified at step 410. Table 5 below showsexemplary types of digital modulation and corresponding crest factorvalues which may be used according to the present invention. TABLE 5Modulation Type Crest Factor (dB) BPSK ½ 4 BPSK ¾ 4 QPSK ½ 4 QPSK ¾ 4 16QAM ½ 6 16 QAM ¾ 6 64 QAM ⅔ 9 64 QAM ¾ 9

As indicated in Table 5, modulation types having higher efficiency perbit tend to have higher crest factor values. Accordingly, the digitalvalue retrieved at step 420 may likewise vary based on the modulationtype. The crest factors shown in FIG. 5 are examples only, and othervalues may also be used according to the present invention.

At step 430, the digital value retrieved at step 420 is converted to ananalog signal. According to an exemplary embodiment, DAC 60 receives thedigital value retrieved by processor 10 at step 420, and converts thedigital value to a corresponding analog signal.

At step 440, the analog signal generated at step 430 is used to controlpower amplifier 50. According to an exemplary embodiment, the analogsignal provided from DAC 60 is applied to power amplifier 50 to therebycontrol the bias current of the final stage of power amplifier 50 (seeFIG. 2). As previously indicated herein, the bias current of the finalstage of power amplifier 50 may be controlled in an adaptive manner tothereby optimize the bias current for the particular type of digitalmodulation employed. Accordingly, the bias current of the final stage ofpower amplifier 50 shown in FIG. 2 may be decreased when decreasing theefficiency per bit of the digital modulation (e.g., when changing themodulation from 64 QAM ¾ to BPSK ½), and likewise may be increased whenincreasing the efficiency per bit of the digital modulation (e.g., whenchanging the modulation from BPSK ½ to 64 QAM ¾).

At step 450, the amplified transmission signal from power amplifier 50is transmitted. According to an exemplary embodiment, signaltransmitting element 70 wirelessly transmits the amplified transmissionsignal. The steps of FIG. 4 may be performed in an iterative manner suchthat processor 10 may detect any change to the type of digitalmodulation used by transmitter apparatus 100, and the bias current ofthe final stage of power amplifier 50 may be controlled in an adaptivemanner based on the type of digital modulation employed.

As described herein, the present invention provides a technique forcontrolling a transmission apparatus which advantageously reduces powerconsumption. Accordingly, the principles of the present invention may beparticularly applicable to apparatuses such as mobile transceivers whichemploy a battery power supply. The reduction of power consumption mayalso help reduce the generation of undesirable heat by such apparatuses.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. For example, the principles of the present inventionmay be applied to apparatuses or devices which support communicationstandards other than the exemplary Hiperlan2, IEEE 802.11a and DVB-Tstandards mentioned herein. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims. As such, it isintended that the present invention only be limited by the terms of theappended claims.

1. An apparatus, comprising modulating means for performingmulti-carrier modulations wherein it further comprises: processing meansfor retrieving a digital value corresponding to type of modulationassociated with a transmission signal; converting means converting saiddigital value to an analog signal, amplifying means for amplifying thetransmission signal, controlled by the analog signal decreasing biascurrent when decreasing the efficiency per bit of the digital modulationand vice versa.
 2. The apparatus of claim 1, further comprising signaltransmitting means for wirelessly transmitting said transmission signal.3. The apparatus of claim 1, wherein said type of modulation includesone of: bi-phase shift keyed modulation; quadrature phase shift keyedmodulation; and quadrature amplitude modulation.
 4. The apparatus ofclaim 1, wherein said transmitter apparatus is part of a mobiletransceiver having a battery power supply.
 5. A method for controlling atransmitter apparatus, comprising: identifying and retrieving a digitalvalue corresponding to a type of digital modulation for a transmissionsignal; converting said digital value to an analog signal; andcontrolling power amplification of said transmission signal using saidanalog signal in decreasing a bias current of the amplifier whendecreasing the efficiency per bit of the digital modulation and viceversa.
 6. The method of claim 5 further comprised of wirelesslytransmitting said transmission signal.
 7. The method of claim 5, whereinsaid digital value is based on the crest factor.
 8. The method accordingto claim 5 wherein bias current is decreased when digital modulation ischanged from 64 QAM ¾ to BPSK ½.
 9. The method according to claim 7wherein it is in compliance with one of the standards belonging to theset comprising: Hiperlan type 2; IEEE 802.11a; DVB-T 802.16a
 10. Themethod of claim 5, wherein said type of digital modulation includes oneof: bi-phase shift keyed modulation; quadrature phase shift keyedmodulation; and quadrature amplitude modulation.
 11. An apparatus,comprising: a processor for retrieving a digital value corresponding totype of modulation associated with a transmission signal; a digitalanalog converter converting said digital value to an analog signal; apower amplifier for amplifying the transmission signal, controlled bythe analog signal decreasing bias current when decreasing the efficiencyper bit of the digital modulation and vice versa.
 12. The apparatus ofclaim 11, further comprising a signal transmitting element operative towirelessly transmit said transmission signal.
 13. The apparatus of claim11, wherein said type of digital modulation includes one of: bi-phaseshift keyed modulation; quadrature phase shift keyed modulation; andquadrature amplitude modulation.
 14. The apparatus of claim 11, furthercomprising a modulator operative to perform a plurality of differenttypes of digital modulation.
 15. The apparatus of claim 11, wherein saidapparatus is embodied as a mobile transceiver having a battery powersupply.